1. Field of the Invention
The present invention relates to a device and method for quantitatively measuring the coating quality of a coated surface.
2. Description of the Prior Art
The coating quality of coated surfaces of a vehicle body or the like has been conventionally measured through the senses such as the sense of sight of a trained workman. This measuring method is defective since it is largely affected by the workman's feeling and obstructs the automation of the production steps of vehicles.
From the above circumstances, devices for objectively measuring the coating quality of the coated surface have been developed.
Examples of these devices are disclosed in Japanese unexamined patent publications Nos. Sho 52-71289 and Sho 58-97608, for example. Each of these devices quantitatively measures the coating quality of the coated surface by positioning a pattern plate having a slit pattern opposite the coated surface and applying light to the coated surface through the slit pattern to form a reflected image of the slit pattern. In this case, the change of sharpness of outlines of the formed reflected image of the slit pattern is quantitatively measured.
Japanese unexamined patent publication No. Sho 52-71289 discloses the steps of slicing the reflected image on a plurality of levels, and detecting the change of the pattern width on each level. In this method, when the pattern width on each level changes by only a small amount, the outline of the reflected image is judged to be sharp, namely the coating quality of the coated surface is judged to be high.
In Japanese unexamined patent publication No. Sho 58-97608, frequency components composing the reflected image are detected. In this method, when the frequency components are on the high frequency side, the outline of the reflected image is judged to be sharp.
However, the device of Japanese unexamined patent publication No. Sho 52-71289 has a problem in that it is extremely difficult to measure slight differences in coating quality between the coated surfaces of high coatings quality. And the device of Japanese unexamined patent publication No. Sho 58-97608 also has a problem in that the calculation for obtaining the frequency components is comparatively complex.